GWYNN CYN

Sections 19,30,31,32 R16W, T9S USGS Telephone Canyon 7.5' Quad; Sections 30,31,32 R16W T9S; Secs. 4.5.9 R16W, T10S USGS Negrito Mtn 7.5' Quad (and see below), Gila National Forest, south central Catron County, New Mexico.

The Gwynn Canyon source was not personally surveyed during the original study. The information and samples used here was provided by Chris Stevenson (then) of New Mexico State University's Obsidian Hydration Laboratory (see also Hughes 1988). The specimens for the original field collection were all procured in Ewe Canyon south of another source area in the Gwynn Canyon area (discovered first; see 2013 collection below). The nodules (at least 5 cm in diameter) are found mainly in a volcanic alluvium and within the washes. The glass is a high quality material, but only 15 nodules were available for study. No specific reduction areas were noted by Stevenson, but most nodules were picked up in the Gwynn Canyon bottom. The 15 nodules studied all have waterworn black cortex and the aphyric glass ranges from an opaque black to a nearly transparent brown. Banding did not occur in this small sample.

There are no known published references on this new source other than the regional geologic map (Weber and Willard 1959).

[updated 1995] In the earlier study (Shackley 1988), this source was not personally mapped or surveyed. My survey in 1993 indicated that marekanites were directly associated with glassy, perlitic rhyolite in Ewe Canyon to the south derived from a dome complex called Feathery Hill on the Telephone Canyon USGS 7.5' Quad. This stream system erodes west toward the San Francisco River. These coalesced domes shown as Feathery Hill on the quadrangle map, exhibit nodule densities in the regolith up to 200 per m². This locality is located in Sections 19 and 20 T9S R16W Telephone Canyon 7.5' Quad 1963, Catron County, New Mexico. Unmodified marekanites on the domes have maximum diameters near 50 mm, although the vast majority (95%) are 30 mm and smaller. Bipolar cores and flakes were found on and near Feathery Hill, but in low densities (<1 per 100 m²).

As noted above, marekanites are eroding into the Ewe Canyon system and possibly the upper San Francisco River. On March 6, 2019 vitrophyric perlitic obsidian (not artifact quality) nodules were recovered from the San Francisco River alluvium at Glenwood, New Mexico. Two of the analyzed samples matched the Gwynn/Ewe Canyon obsidian source, so artifact quality obsidian from that source potentially enters the San Francisco River system, probably through Negrito Creek into the Tularosa River then the San Francisco River south or Reserve. The pieces recovered in the San Francisco River at Glenwood are certainly derived from the perlite above Negrito Creek at Gwynn Canyon (see map here). Published references for the geology of this source include Findlow and Bolognese (1982:56), the regional geology map by Weber and Willard (1959), and Ratté et al. (1984).

The Gwynn Canyon and two of the Mule Creek groups (Antelope Creek and Mule Mountains) are very similar in trace element composition. Zirconium plotted against Nb, Y, and/or Ba is the best method to discriminate these sources using EDXRF. This can be an important issue in western New Mexico late prehistory because these sources are located in very different environments that may have had cultural significance in prehistory. It is possible that in the late period Gwynn Canyon obsidian could have been controlled by the Cibola branch of the Mogollon while the Mule Creek sources could have been controlled by the Mimbres branch. This may or may not influence the spatial distribution of these obsidian sources in the region and confident source assignment can become crucial. Again, the secondary distribution of Mule Creek is quite extensive to the west through the San Francisco and Gila River systems, and the presence of Mule Creek glass in archaeological contexts to the west may not necessarily indicate that it was procured in the highlands, but could have been procured from the Gila River alluvium (see Shackley 2005). See the Mule Creek page for further discussion here

Table 1. Elemental concentrations for the "original" Gwynn Canyon source standards, and the 2013 sample. Samples GC 11-20 from Feathery Hill at the head of Ewe Canyon, the rest (GC 1-10) are from secondary samples from Gwynn Canyon submitted by Chris Stevenson. All measurements in parts per million (ppm)

SAMPLE	Mn	Zn	Rb	Sr	Y	Zr	Nb	Ba	Pb	Th
2013 samples
Feathery Hill
092813-1-1	376	47	208	24	30	145	24	54	27	28
092813-1-2	379	41	215	23	27	139	21	54	26	36
092813-1-3	445	54	235	22	29	151	23	99	31	37
092813-1-4	388	42	211	19	30	150	19	46	27	26
092813-1-5	396	51	222	21	35	149	23	24	28	28
Gwynn Canyon dome
092813-2-1-1	545	38	206	22	31	145	22	63	28	34
092813-2-1-2	370	53	218	21	33	140	25	35	27	36
092813-2-1-3	466	61	239	24	29	151	21	<1	36	31
092813-2-1-4	406	57	219	20	33	142	19	65	29	32
092813-2-1-5	337	53	211	21	28	143	22	39	27	32
092813-2-1-6	370	63	209	22	28	150	20	50	30	32
2ndary deposit Gwynn Canyon
092813-2-2-1 (perlite sample)	449	54	227	23	33	154	26	60	28	35
092813-2-2-2	453	51	243	25	32	153	23	43	32	33
092813-2-2-3	390	53	216	22	30	145	21	60	28	29
092813-2-2-4	426	58	221	25	35	145	29	88	31	35
092813-2-2-5	348	43	205	21	32	139	25	25	28	25
0-2813-2-2-6	432	53	227	21	31	144	22	26	23	43
original samples - 1993
GC-1	418		237	20	31	161	23	86
GC-2	459		243	21	30	159	27	85
GC-3	438		228	19	30	154	22	85
GC-4	414		216	18	33	153	20	90
GC-5	414		221	23	32	166	18	94
GC-6	453		229	19	31	152	26	87
GC-7	454		237	22	31	155	21	87
GC-8	427		226	18	31	150	23	86
GC-9	446		221	17	33	167	21	87
GC-10	417		220	16	29	151	23	82
GC11	420		231	21	30	158	22	78
GC12	508		244	21	32	164	24	78
GC13	460		237	19	33	156	21	81
GC14	363		196	18	28	137	20	88
GC15	376		223	17	28	151	21	77
GC16	415		230	18	31	158	21	81
GC17	501		243	20	32	162	22	80
GC18	328		198	18	27	144	17	91
GC19	456		227	21	36	163	24	108
GC20	414		222	19	34	150	15	80
RGM1-S4 (USGS)	273	37	147	106	24	216	8	865	19	17

Table 2. Mean and central tendency for the Gwynn and Ewe Canyon samples

	N	Minimum	Maximum	Mean	Std. Deviation
Mn	37	328	545	420	47
Fe	37	7368	10860	8980	782
Zn	17	38	63	51	7
Rb	37	196	244	223	13
Sr	37	16	25	21	2
Y	37	27	36	31	2
Zr	37	137	167	151	8
Nb	37	15	29	22	3
Pb	17	23	36	29	3
Th	17	25	43	32	5

Table 3. Oxide values for one sample from dome complex in Gwynn Canyon (see map below)

Sample	SiO₂	Al₂O₃	CaO	Fe₂O₃	K₂O	MgO	MnO	Na₂O	TiO₂
092813-2-2-2	75.709	11.375	0.608	1.265	6.037	0	0.094	4.456	0.206
RGM1-S4	74.501	12.051	1.505	2.294	5.182	0	0.053	3.874	0.293

Sr, Rb, and Zr concentration plot of the Gwynn Canyon and Mule Creek sources. Note the genetic similarity.

On this date Jeff Ferguson and I re-surveyed the Gwynn/Ewe Canyon area and Feathery Hill and collected more samples. The location and general character of the Feathery Hill locality eroding into Ewe Canyon was confirmed, but another locality to the northwest above Negrito Creek in Gwynn Canyon was located that produced artifact quality marekanites. Initial survey of Gwynn Canyon above this locality at UTM 12S 0728596/3713894 ± 3m, indicated that no obsidian was present in Gwynn Canyon. Below the above noted locality however, abundant marekanites are entering Negrito Creek in Gwynn Canyon and possibly eroding into upper San Francisco River. This locality is a dome complex consisting of perlitic lava near the military crest of the domes with a thin lahar below. While no marekanites were found in-situ in the perlite, there were marekanites in the perlitic sand eroding directly from the perlitic lava. The marekanites up to about 30 mm down to pea size were found in a small wash eroding into Negrito Creek. The Feathery Hill obsidian erodes south through Ewe Canyon, while the obsidian in Gwynn Canyon is eroding west through Negrito Creek potentially into the San Francisco River system (see map below).

The elemental composition between these localities is similar (see Tables 1 and 2). A perlite sample analyzed from the dome complex on the north side of Gwynn Canyon is well within the range of variability indicating that the marekanites recovered are from the same magma source, although none were located in-situ.

The 2013 collection also expanded the character (opacity, sphericity) of these marekanites at the source. All of the marekanites from both localities are sub-rounded. A few of the samples from Feathery Hill are entirely mahogany to black/mahogany, not seen in the earlier collections or noticed in the archaeological record. The character varies from nearly opaque black to nearly transparent with black banding. There is no detectable elemental differences between colors.

Findlow, F.J., and M. Bolognese, 1982, A preliminary analysis of prehistoric obsidian use within the Mogollon area. In P.H. Beckett (Ed.) Mogollon Archaeology: Proceedings of the 1980 Mogollon Conference, pp. 297-316. Ramona, California: Acoma Press.

Hughes, R.E., 1988, Archaeological significance of geochemical contrasts among southwestern New Mexico obsidians. Texas Journal of Science 40:297-307.

Ratté, J.C., R.F. Marvin, and C.W. Naeser, 1984, Calderas and ash flow tuffs of the Mogollon Mountains, southwestern New Mexico. Journal of Geophysical Research 89:87113-8732.

Shackley, M.S., 1988, Sources of archaeological obsidian in the Southwest: an archaeological, petrological, and geochemical study. American Antiquity 53:752-772.

Shackley, M.S., 2005, Obsidian: Geology and Archaeology in the North American Southwest. Tucson: University of Arizona Press.

Weber, R.H., and M.E. Willard, 1959, Reconnaissance geologic map of Mogollon 30 minute quadrangle. New Mexico Institute of Mining and Technology, Socorro.